The present invention relates to apparatus for building a continuous tobacco stream, and more particularly to improvements in apparatus of the type wherein the tobacco stream is built up at one side of an elongated reach of an endless foraminous conveyor and wherein the other side of the elongated reach is adjacent to a suction chamber serving to attract the particles to the one side of the reach or against the particles of the growing tobacco stream. In such apparatus, the elongated reach of the conveyor closes one end of a channel wherein the particles of tobacco advance under the action of mechanical propelling means or with a gaseous carrier medium, preferably air.
It is already known to provide stream forming apparatus of the above outlined character with means for causing tobacco particles which approach the foraminous conveyor to move in a direction having a component of movement in the direction of lengthwise movement of the elongated reach of the foraminous conveyor. This reduces the likelihood of rebounding of tobacco particles on impact against the conveyor or against the growing tobacco stream on the conveyor. Optimum conditions for the building of a satisfactory tobacco stream would be established if the aforementioned component of movement of tobacco particles were equal or would closely approximate the speed of forward or lengthwise movement of the tobacco collecting reach of the foraminous conveyor, i.e., if the relative movement between arriving tobacco particles and the foraminous conveyor and/or the growing stream were zero or close to zero. U.S. Pat. No. 3,030,965 discloses an apparatus wherein a current of air transports tobacco particles upwardly against the underside of the elongated lower reach of a foraminous belt conveyor. The particles are transported in a channel whose inclination with respect to the direction of movement of the lower reach is such that the paths of the particles (or at least of some of the particles) of tobacco are caused to make an acute angle with the direction of movement of the lower reach. The direction of movement of particles is constant all the way from the locus where they enter the tobacco channel to the underside of the lower reach of the foraminous conveyor. A suction chamber above the lower reach of the conveyor attracts the particles to the underside of the lower reach or to the particles of the tobacco stream which grows at the underside of such lower reach.
A drawback of the just described conventional stream building apparatus is that the foraminous conveyor will accumulate a satisfactory tobacco stream only as long as its speed is below a certain relatively low limit. Once the speed limit is exceeded, a satisfactory stream would develop only if the speed of ascending air were increased beyond a value which can be achieved in such types of apparatus. The speed of the air current is limited by the relatively small cross-sectional area of the tobacco channel wherein the particles of tobacco advance toward the lower reach of the foraminous conveyor and also by the resistance which the foraminous conveyor and the growing tobacco stream thereon offer to the passage of ascending air currents into the suction chamber. Furthermore, the angle between the tobacco channel and the lower reach of the foraminous conveyor cannot be reduced at will for a number of reasons.